Comparative evaluation of power factor improvement techniques for squirrel cage induction motors

The authors describe the results obtained from a series of tests of relatively simple methods of improving the power factor of squirrel-cage induction motors. The methods, which are evaluated under controlled laboratory conditions for a 10 HP, high-efficiency motor, include terminal voltage reduction, terminal static capacitors, and a floating winding with static capacitors. Each of these techniques is tested over a range of torques from zero load up to 150% of rating. The effects of the different configurations on starting performance, pull-out torque, and operating efficiency are also considered. The test results are compared with equivalent circuit model predictions that are then used to identify optimum conditions for each of the power factor improvement techniques compared with the basic inductor motor. The relative economic values and the implications of component failures of the three methods are discussed